Subject: Re: linux-next: build failure after merge of the origin tree

From: Kees Cook <[email-masked]>
Date: Wed, 29 Jul 2020 20:17:48 -0700

On Wed, Jul 29, 2020 at 04:43:04PM -0700, Linus Torvalds wrote:
> On Wed, Jul 29, 2020 at 4:08 PM Stephen Rothwell <[email-masked]> wrote:
> >
> > include/linux/random.h:123:24: error: variable 'net_rand_state' with 'latent_entropy' attribute must not be local
> >   123 | DECLARE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
> 
> Hmm.
> 
> Ok, this shows a limitation of my allmodconfig testing (and all my
> normal builds) - no plugins. So that problem wasn't as obvious as it
> should have been.

I'll look into this more tomorrow. (But yes, __latent_entropy is
absolutely used for globals already, as you found, but this is the first
percpu it was applied to...)

> Adding the gcc plugin people. Otherwise the only option seems to be to
> just remove that __latent_entropy marker.

And just another heads-up, the patch[1] (which was never sent to a public
list) also breaks arm64 (circular header needs?):

$ make CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 defconfig
...
$ make -j$(getconf _NPROCESSORS_ONLN) CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64
...
In file included from ./arch/arm64/include/asm/smp.h:33,
                 from ./include/linux/smp.h:82,
                 from ./include/linux/percpu.h:7,
                 from ./include/linux/random.h:14,
                 from arch/arm64/kernel/pointer_auth.c:5:
./arch/arm64/include/asm/pointer_auth.h: In function ‘ptrauth_keys_init_user’:
./arch/arm64/include/asm/pointer_auth.h:40:3: error: implicit declaration of function ‘get_random_bytes’; did you mean ‘get_random_once’? [-Werror=implicit-function-declaration]
   40 |   get_random_bytes(&keys->apia, sizeof(keys->apia));
      |   ^~~~~

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f227e3ec3b5cad859ad15666874405e8c1bbc1d4

-- 
Kees Cook